This double-blind study will compare the efficacy and safety of oral 256U87 with matching placebo for the treatment of herpes zoster in immunocompetent adults who are less than 50 years of age. Otherwise normal adults with localized herpes zoster presenting within 72 hours of the onset of vesicles will be randomized to receive either 256U87, 1000mg orally or matching placebo, three times a day for 7 days. Patients will be evaluated for a total of six months.